public   void EnableDHCP()
        {

            string ethernetDescription = "{5F632379-D5A7-4F26-89FC-C172212EDF65}";
            ManagementClass wmi = new ManagementClass("Win32_NetworkAdapterConfiguration");
            ManagementObjectCollection moc = wmi.GetInstances();
            foreach (ManagementObject mo in moc)
            {
                //如果没有启用IP设置的网络设备则跳过
                /* if (!(bool)mo["IPEnabled"])
                       continue;*/
                string settingID = mo["SettingID"].ToString();
                string descrption = mo["Description"].ToString();
                if (settingID == ethernetDescription)
                { //重置DNS为空
               
                    mo.InvokeMethod("SetDNSServerSearchOrder", null);
                    //开启DHCP
                    mo.InvokeMethod("EnableDHCP", null);
                }
            }